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#include <cstdio>
#include <vector>
#include <algorithm>

const int max_n = 200;
const double eps = 1e-12;
const int max_m = 2000000;



double eq(double x, double y) {
  double diff = x - y;
  if (diff < 0) diff = -diff;
  return diff < eps;
}

double lt(double x, double y) {
  return x + eps < y;
}

struct Point {
  double x, y;

  bool operator<(const Point& other) const {
    return lt(x, other.x) || eq(x, other.x) && lt(y, other.y);
  }
};

int n, top;
Point A[max_n];
Point B[max_n];
int stack[max_m];

std::vector<Point> good_points;
std::vector<Point> points;
std::vector<Point> convex_hull;

double vec(double v_x, double v_y, double u_x, double u_y) {
  return v_x * u_x + v_y * u_y;
}

double scal(double v_x, double v_y, double u_x, double u_y) {
  return v_x * u_y - v_y * u_x;
}

struct Direction {
  Direction(double _x, double _y, bool _o) : vx(_x), vy(_y), open(_o) {
    if (eq(vx, 0)) {
      if (vy > -eps) quarter = 1, angle = 0.0;
      else quarter = 3, angle = 0.0;
    } else if (vx > eps) {
      if (eq(vy, 0.0)) quarter = 0, angle = 0.0;
      else if (vy > eps) quarter = 0, angle = vy / vx;
      else quarter = 3, angle = -vx / vy;
    }
    else {
      if (eq(vy, 0.0)) quarter = 2, angle = 0.0;
      else if (vy > eps) quarter = 1, angle = -vx / vy;
      else quarter = 2, angle = vy / vx;
    }
  }
  double vx, vy;
  bool open;
  int quarter;
  double angle;

  bool operator<(const Direction& other) const {
    return quarter < other.quarter || quarter == other.quarter && lt(angle, other.angle) || quarter == other.quarter && eq(angle, other.angle) && open && !other.open;
  }
};

std::vector<Direction> dirs;

bool inside(double open_x, double open_y, double close_x, double close_y) {
  // 1.0 , 0.0 vector
  double sco = scal(open_x, open_y, 1.0, 0.0);
  if (sco < -eps) return false;
  if (eq(sco, 0.0) && vec(open_x, open_y, 1.0, 0.0) > eps) return false;
  double scc = scal(1.0, 0.0, close_x, close_y);
  if (scc < -eps) return false;
  if (eq(scc, 0.0) && vec(close_x, close_y, 1.0, 0.0) < -eps) return false;
  return true;
}

bool is_good(Point p) {
//  printf("CAN=%.4lf %.4lf\n", p.x, p.y);
  dirs.clear();
  int start_bilans = 0;
  for (int i = 0; i < n; ++i) {
    double v_x = A[i].x - p.x;
    double v_y = A[i].y - p.y;
    double lv_x = -v_y;
    double lv_y = v_x;
    double rv_x = v_y;
    double rv_y = -v_x;

    double u_x = B[i].x - p.x;
    double u_y = B[i].y - p.y;
    double lu_x = -u_y;
    double lu_y = u_x;
    double ru_x = u_y;
    double ru_y = -u_x;

//    printf("==%.5lf %.5lf %.5lf %.5lf\n", lv_x, lv_y, rv_x, rv_y);
//    printf("==%.5lf %.5lf %.5lf %.5lf\n", lu_x, lu_y, ru_x, ru_y);

    if (eq(u_x, 0.0) && eq(u_y, 0.0)) {
      Direction open(rv_x, rv_y, true);
      dirs.push_back(open);
      Direction close(lv_x, lv_y, false);
      dirs.push_back(close);
//      printf("1. %.5lf %.5lf %.5lf %.5lf\n", open.vx, open.vy, close.vx, close.vy);
      if (inside(open.vx, open.vy, close.vx, close.vy)) ++start_bilans;
      continue;
    }
    if (eq(v_x, 0.0) && eq(v_y, 0.0)) {
      Direction open(ru_x, ru_y, true);
      dirs.push_back(open);
      Direction close(lu_x, lu_y, false);
      dirs.push_back(close);
//      printf("2. %.5lf %.5lf %.5lf %.5lf\n", open.vx, open.vy, close.vx, close.vy);
      if (inside(open.vx, open.vy, close.vx, close.vy)) ++start_bilans;
      continue;
    }

    if (scal(rv_x, rv_y, lu_x, lu_y) > 0.0) {
      Direction open(rv_x, rv_y, true);
      dirs.push_back(open);
      Direction close(lu_x, lu_y, false);
      dirs.push_back(close);
//      printf("3. %.5lf %.5lf %.5lf %.5lf\n", open.vx, open.vy, close.vx, close.vy);
      if (inside(open.vx, open.vy, close.vx, close.vy)) ++start_bilans;
    }
    else {
      Direction open(ru_x, ru_y, true);
      dirs.push_back(open);
      Direction close(lv_x, lv_y, false);
      dirs.push_back(close);
//      printf("4. %.5lf %.5lf %.5lf %.5lf\n", open.vx, open.vy, close.vx, close.vy);
      if (inside(open.vx, open.vy, close.vx, close.vy)) ++start_bilans;
    }
  }

  std::sort(dirs.begin(), dirs.end());
  for (int i = 0; i < dirs.size(); ++i) {
//    printf("$ %.4lf %.4lf %d %d %.4lf\n", dirs[i].vx, dirs[i].vy, dirs[i].open, dirs[i].quarter, dirs[i].angle);
    if (dirs[i].open) ++start_bilans;
    else --start_bilans;
    if (start_bilans == 0) return false;
  }
  return true;
}

bool find_intersection(const Point& x_1, const Point& x_2, const Point& y_1, const Point& y_2, Point& result) {
  double A_1 = x_2.y - x_1.y;
  double B_1 = x_1.x - x_2.x;
  double C_1 = A_1 * x_1.x + B_1 * x_1.y;

  double A_2 = y_2.y - y_1.y;
  double B_2 = y_1.x - y_2.x;
  double C_2 = A_2 * y_1.x + B_2 * y_1.y;

  double det = A_1 * B_2 - A_2 * B_1;

  if (eq(det, 0)) return false;

  result.x = (B_2 * C_1 - B_1 * C_2) / det;
  result.y = (A_1 * C_2 - A_2 * C_1) / det;
  return true;
  if (lt(x_1.x, x_2.x)) {
    return x_1.x < result.x && result.x < x_2.x;
  }
  if (lt(x_2.x, x_1.x)) {
    return x_2.x < result.x && result.x < x_1.x;
  }

  if (lt(x_1.y, x_2.y)) {
    return x_1.y < result.y && result.y < x_2.y;
  }
  return x_2.y < result.y && result.y < x_1.y;
}

double skret(Point a, Point b, Point c) {
  return (a.x - c.x) * (b.y - c.y) - (a.y - c.y) * (b.x - c.x);
}

int main() {
  scanf("%d", &n);
  std::vector<Point> pp;
  for (int i = 0; i < n; ++i) {
    scanf("%lf %lf %lf %lf", &A[i].x, &A[i].y, &B[i].x, &B[i].y);
    pp.push_back(A[i]);
    pp.push_back(B[i]);
  }
  /*
  for (double x = -20.0; x < 20.0; x += 0.0001) {
    for (double y = -20.0; y < 20.0; y += 0.0001) {
      Point p;
      p.x = x;
      p.y = y;
      if (is_good(p)) {
        printf("good at %.5lf %.5lf\n", x, y);
      }
    }
  }
  return 0;*/
  for (int i = 0; i < pp.size(); ++i) {
    for (int j = i + 1; j < pp.size(); ++j) {
      for (int k = i + 1; k < pp.size(); ++k) {
        for (int r = k + 1; r < pp.size(); ++r) {
          Point intersect;
          if (find_intersection(pp[i], pp[j], pp[k], pp[r], intersect) && is_good(intersect)) good_points.push_back(intersect);
        }
      }
    }
  }
  /*
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      if (j == i) continue;
      Point intersect;
      if (find_intersection(A[i], B[i], A[j], B[j], intersect) && is_good(intersect)) good_points.push_back(intersect);
      for (int k = 0; k < n; ++k) {
        if (k == i || k == j) continue;
        if (find_intersection(A[i], A[j], B[i], A[k], intersect) && is_good(intersect)) good_points.push_back(intersect);
        if (find_intersection(A[i], A[j], B[i], B[k], intersect) && is_good(intersect)) good_points.push_back(intersect);
        if (find_intersection(A[i], B[j], B[i], A[k], intersect) && is_good(intersect)) good_points.push_back(intersect);
        if (find_intersection(A[i], B[j], B[i], B[k], intersect) && is_good(intersect)) good_points.push_back(intersect);
      }
    }
  }
  */
  std::sort(good_points.begin(), good_points.end());
  for (int i = 0; i < good_points.size(); ++i) {
    if (i == 0 || !eq(good_points[i].x, good_points[i - 1].x) || !eq(good_points[i].y, good_points[i - 1].y)) {
      points.push_back(good_points[i]);
    }
  }
  /*
  for (int i = 0; i < points.size(); ++i) {
    printf("G: %.4lf %.4lf\n", points[i].x, points[i].y);
  }
 */
  top = 0;
  for (int i = 0; i < points.size(); ++i) {
    while (top > 1 && skret(points[i], points[stack[top - 1]], points[stack[top - 2]]) > eps) {
      --top;
    }
    stack[top++] = i;
  }
  for (int i = 0; i < top; ++i) {
    convex_hull.push_back(points[stack[i]]);
  }
  top = 0;
  for (int i = points.size(); i > 0; --i) {
    while (top > 1 && skret(points[i - 1], points[stack[top - 1]], points[stack[top - 2]]) > eps) {
      --top;
    }
    stack[top++] = i - 1;
  }
  for (int i = 0; i < top; ++i) {
    convex_hull.push_back(points[stack[i]]);
  }
  double result = 0.0;
  for (int i = 0; i + 1 < convex_hull.size(); ++i) {
//    printf("X: %lf %lf\n", convex_hull[i].x, convex_hull[i].y);
    result += convex_hull[i].x * convex_hull[i + 1].y - convex_hull[i].y * convex_hull[i + 1].x;
  }
  result /= 2.0;

  printf("%.12lf\n", result);
  
  return 0;
}